The present invention relates to a method for rotating a disc-shaped object, such as a wafer, wherein along a side of said object a gas flow is directed, giving a rotation to said object, wherein said gas flow is given the rotation generating component being tangential to said object by a pattern of grooves.
Such a method is known from U.S. Pat. No. 3,706,475. In this specification a device is disclosed for transporting wafers. The device comprises an elongated trajectory and from the lower side gas is added in such a way that except from a transferring movement also a rotating movement is given to the wafer.
From U.S. Pat. No. 393,068 a method is known for rotating an object such as a wafer from semi conducting material placed in a reactor. During the treatment of a single wafer which is held floating in a reactor, it is important for a treatment of this nature to be carried out as uniformly as possible. For this purpose, it is proposed, in the prior art, to impart a rotational movement to the wafer. This rotational movement is imposed, according to the prior art, by having the gas-introduction openings opening out not perpendicular to the wafer surface, but rather having them end at an acute angle with respect to the wafer surface (xe2x80x9cdirectional air jetsxe2x80x9d). As a result, a propulsive movement is imparted to the wafer.
However, drilling the gas-introduction openings in this way has proven to be particularly complicated while. in addition, the rotational speed which can be achieved is limited. owing to the fact that the gas which flows out very quickly loses its tangential flow component. Moreover, reactor walls of this nature are complicated to produce, since openings have to be drilled at an angle with respect to the wall.
The object of the present invention is to avoid these drawbacks while nevertheless maintaining the rotation of the wafer and making it possible, in a relatively inexpensive and simple manner, to impose a rotation of this nature on the wafer.
It is a further aim of the subject invention to accurately position the wafer to realise effective treatment thereof.
This aim is realised with the method as described above in that, said object is floatingly received in a compartment being closed on all sides, said object being substantially rotating only and in that along the other side of said object, a further gas flow is directed.
Through the presence of a groove pattern the gas flow is given a component of movement extending tangentially to the wafer, i.e. gives a rotating movement to the wafer. Furthermore, the wafer is subjected from the other side to a further gas flow, so that this is accurately positioned in the reactor. Also the gas flows are controlled and provided such that the wafer substantially only rotates and does not execute a translating movement.
According to a preferred embodiment gas flow is blown in a direction substantially perpendicular to said object from a seas introduction opening in the reactor.
Surprisingly, it has been found that by providing a pattern of grooves it is possible to affect the direction of flow of the gas. The gas will preferably begin to flow in the direction of the groove, since this is the path of least resistance. The gas flow is guided in this way over the entire distance which the groove covers. If the direction of the groove contains a tangential component, a tangential flow component is also imparted to the gas. This tangential flow component imposes rotation on the wafer. Grooves of this nature can be produced relatively easily by milling. The pattern of grooves may have any desired shape. According to an advantageous design, the pattern of grooves is arranged in the shape of a spiral. In this case, the grooves are preferably arranged in such a manner that the spiral starts in the vicinity of the center of the wafer and ends in the vicinity of the circumferential edge thereof. The desired rotational speed can be set by means of the shape of the spiral grooves. The total quantity of gas supplied to the wafer can therefore be selected independently of the desired rotational speed and can be set in such a manner that optimum axial and radial support and a uniform process result can be obtained. This can be achieved by adapting the shape of the spiral grooves. As a result, it is possible to work with comparatively small quantities of gases, as is desirable in order to maintain the uniformity inside the reactor.
This uniformity, can be increased still further by also arranging the openings from which the gases emerge in a spiral pattern. This means that, according to a preferred embodiment, the openings extend essentially perpendicular to the surface of the wafer, but if these openings are joined by an imaginary line, the result is a spiral whose origin preferably also lies in the vicinity of the desired center of the wafer and whose end lies in the vicinity of the circumferential edge thereof. During rotation, a point on the wafer does not always xe2x80x9cseexe2x80x9d the same openings arranged in a circle, which in the prior art causes an annular treatment pattern.
The combination of the rotation and the spiral pattern of gas-introduction openings results in a particularly uniform distribution of the treatment gases and a particularly uniform treatment of the wafer surface.
Another possible design of the pattern of grooves consists in constructing this pattern from one or more circle segments. In this case, it is important for a gas-introduction opening to be situated in the vicinity of one of the ends of the groove. In this case too, the gas flow will preferably begin to flow in the direction of the groove. Since the direction of the groove is perfectly tangential, this method of rotational driving has proven particularly effective. Another advantage of this variant is that the rotational driving is virtually independent of the axial bearing of the wafer or, in other words, of the gas flow which keeps the wafer floating. For example, it is possible to increase or interrupt the gas flow for providing the rotational drive, while the gas flow for keeping the wafer floating is maintained at a constant level. As a result, the rotational speed of the wafer changes, while the other conditions in the reactor remain virtually unchanged. Positioning the grooves, which are arranged as circle segments, in the vicinity of the edge of the wafer maximizes the drive moment and the efficiency of the rotational drive. Also arranging a gas-discharge opening in the vicinity of the other end of the groove further increases the efficiency of the rotational drive. The direction of rotation is reversed by reversing the direction of flow of the gas through the rotational drive groove.
According to a further preferred embodiment the gas flow imposing rotation to the wafer is, in the case that the wafer is in horizontal position in the reactor, introduced at the upper side of the wafer. I.e. rotational drive can be realised both from above, from below as well as from both sides.
The invention also relates to a reactor for the floating, rotational treatment of semiconductor wafers, comprising a top part and a bottom part, between which a chamber which accommodates the wafer is delimited, the said top part and bottom part being provided with gas-supply openings, the gas-introduction openings extending essentially perpendicular to the top part and/or bottom part and a pattern of grooves, which imparts to the said gas flow a component which is tangential with respect to the said object, being arranged in at least one of the said parts.